HI!!!!!

So today, I went running after work in my neighborhood, and it struck me as odd that no one says hi. I passed a couple people, and would attempt to make eye contact and they just wouldn't budge. I was as if I was George Bush or something....
Once I started to think about it though I realized they probably aren't saying hi to me because I am not open to their hello.
So my sociology experiment began. As I was running up this hill a guy was bringing his trash out to the street, so I looked up and said "HI!" and he said "Hi! How are you?" and I said "good!" then not 2 seconds later I saw another person and said "Hi!" and she said "Hi!".
So, as of today my conclusion for my experiment is that people only say hi when you either say hi or you smile and let them say hi to you first.
Tomorrow, if I run, I will test the same theory. Every other person I run by I will say hi, and every other person I will not. My hypothesis for this experiment is that everyone I say hi to will say hi back, however those I do not say hi to will not say anything.
But here is my question...Why can't they say hi to me first? Why is it that I have to say hi, isn't anyone nice anymore?